public static TraceTagCollection ParseFromPropagationHeader(string?propagationHeader)
{
if (string.IsNullOrEmpty(propagationHeader))
{
return(new TraceTagCollection());
}
var tags = propagationHeader !.Split(TagPairSeparators, StringSplitOptions.RemoveEmptyEntries);
var tagList = new List <KeyValuePair <string, string> >(tags.Length);
var cacheOriginalHeader = true;
foreach (var tag in tags)
{
// the shortest tag has the "_dd.p." prefix, a 1-character key, and 1-character value (e.g. "_dd.p.a=b")
if (tag.Length >= MinimumPropagationHeaderLength &&
tag.StartsWith(PropagatedTagPrefix, StringComparison.Ordinal))
{
// NOTE: the first equals sign is the separator between key/value, but the tag value can contain
// additional equals signs, so make sure we only split on the _first_ one. For example,
// the "_dd.p.upstream_services" tag will have base64-encoded strings which use '=' for padding.
var separatorIndex = tag.IndexOf(KeyValueSeparator);
// "_dd.p.a=b"
// ⬆ separator must be at index 7 or higher and before the end of string
// 012345678
if (separatorIndex > PropagatedTagPrefixLength &&
separatorIndex < tag.Length - 1)
{
// TODO: implement something like StringSegment to avoid allocating new strings?
var key = tag.Substring(0, separatorIndex);
var value = tag.Substring(separatorIndex + 1);
tagList.Add(new KeyValuePair <string, string>(key, value));
}
else
{
// skip invalid tag
cacheOriginalHeader = false;
}
}
else
{
// skip invalid tag
cacheOriginalHeader = false;
}
}
var traceTags = new TraceTagCollection(tagList);
if (cacheOriginalHeader)
{
// we didn't skip any invalid tag, we can cache the original header string
traceTags._cachedPropagationHeader = propagationHeader;
}
return(traceTags);
}
private int WriteTraceTags(ref byte[] bytes, ref int offset, TraceTagCollection tags, ITagProcessor[] tagProcessors)
{
int count = 0;
if (tags != null)
{
lock (tags)
{
count += tags.Count;
// don't cast to IEnumerable so we can use the struct enumerator from List<T>
foreach (var tag in tags)
{
WriteTag(ref bytes, ref offset, tag.Key, tag.Value, tagProcessors);
}
}
}
return(count);
}